Lecture on the Importance of Water in Biological Systems

Introduction

• Water is a critical component of life on Earth.
• First life forms originated and evolved in water.
• Water is the medium for biological processes.

Structure and Polarity of Water

• Water molecules: composed of 2 hydrogen atoms and 1 oxygen atom.
• Water molecules are polar due to asymmetrical structure and polar covalent bonds.
  • Oxygen is more electronegative, pulling electrons closer.
  • Creates partial negative and positive charges on opposite sides of the molecule.
• Polarity leads to hydrogen bonding between water molecules.

Importance of Water’s Polarity

• Hydrogen Bonds: Weak bonds formed between the oxygen of one water molecule and hydrogen of another.
• Cohesion: Water molecules stick to each other due to hydrogen bonds.
  • Critical for water transport in plants (e.g., xylem tissue) and organisms like water striders.
• Adhesion: Water's tendency to stick to other surfaces.
  • Important in soil and plant xylem for water transport through capillary action.

Solvent Properties of Water

• Water's polarity makes it a universal solvent.
  • Dissolves polar substances and ions (e.g., salt in water).
• Metabolism and Transport:
  • Supports cellular reactions and movement of substances in organisms (e.g., blood plasma, plant xylem).
• Hydrophobic Molecules:
  • Nonpolar molecules do not dissolve, contributing to cell membrane integrity.

Physical Properties of Water

1. Specific Heat
   • Water has a high specific heat (4.186 J/g°C).
   • Stabilizes temperature in organisms and environments.
2. Thermal Conductivity
   • Water transfers heat effectively.
   • Example: Fennec fox uses blood vessels in ears for cooling.
3. Buoyancy
   • Water's density affects whether objects float or sink.
   • Example: Algae use buoyancy for optimal sunlight exposure.
4. Viscosity
   • Describes a fluid's resistance to flow.
   • Affected by solutes, important in oceanic organisms.

Case Studies

• Black-throated Loon (Gavia Arctica) and Ringed Seal (Pusa Hispira):
  • Comparisons of how physical properties of water affect these organisms.
  • Loon: Moves through air with less resistance.
  • Seal: Faces higher viscosity and heat conductivity in water.
  • Adaptations: Seal's thick fur for temperature regulation.

Conclusion

• Understanding water's properties is crucial for comprehending biological systems and adaptations.
• Exam preparation: Know specific organism examples and properties of water.